Fragment(10)FragmentTransaction.add(id,Fragment)报错: No view found for id 0x****** for fragment

06-26 22:54:28.509: E/AndroidRuntime(20363): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.exe.custommenu/com.exe.custommenu.MainActivity}: java.lang.IllegalArgumentException: No view found for id 0xaabbcc for fragment LeftFrgmt{42956258 #0 id=0xaabbcc}

public class MainActivity extends Activity {
    private MainUI mainui;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mainui = new MainUI(this);
        setContentView(mainui);
        if (savedInstanceState == null) {
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.add(MainUI.LEFT_ID,new LeftFrgmt());//报错
            ft.add(MainUI.MIDEELE_ID, new MiddleFrgmt());
            ft.add(MainUI.RIGHT_ID, new Fragment());
            ft.commit();
        }
    }
}

public class MainUI extends RelativeLayout {
    private Context context;
    private FrameLayout leftMenu;
    private FrameLayout middleMenu;
    private FrameLayout rightMenu;
    private FrameLayout middleMask;
    private Scroller mScroller;
    public static final int LEFT_ID = 0xaabbcc;
    public static final int MIDEELE_ID = 0xaaccbb;
    public static final int RIGHT_ID = 0xccbbaa;

    public MainUI(Context context) {
        super(context);
        initView(context);
    }

    public MainUI(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView(context);
    }

    private void initView(Context context) {
        this.context = context;
        mScroller = new Scroller(context, new DecelerateInterpolator());
        leftMenu = new FrameLayout(context);
        middleMenu = new FrameLayout(context);
        rightMenu = new FrameLayout(context);
        middleMask = new FrameLayout(context);
        leftMenu.setBackgroundColor(Color.RED);
        middleMenu.setBackgroundColor(Color.GREEN);
        rightMenu.setBackgroundColor(Color.RED);
        middleMask.setBackgroundColor(0x88000000);
        leftMenu.setId(LEFT_ID);
        middleMenu.setId(MIDEELE_ID);
        rightMenu.setId(RIGHT_ID);
        addView(leftMenu);
        addView(middleMenu);
        addView(rightMenu);
        addView(middleMask);
        middleMask.setAlpha(0);
    }
        //...
}